Cell Membranes- Cell Membrane Structure

Question 1

What is the function of cell membranes?

Answer 1

A barrier between the cell and the environment a controls which substances enter and leave the cell

Question 2

What does it mean that cell membranes are partially perrmeable?

Answer 2

They allow some molecules through but not others

Question 3

How can substances move across the cell-surface membrane?

Answer 3

Diffusion, osmosis and active transport

Question 4

Why was the fluid mosaic model suggested?

Answer 4

To describe the arrangement of molecules in the membrane

Question 5

What do phospholipid molecules do in the membrane?

Answer 5

Form a continuous double layer (bilayer)

Question 6

Why is the bilayer fluid?

Answer 6

The phospholipids are constantly moving

Question 7

Why is the membrane a mosaic?

Answer 7

There are many different molecules

Question 8

What molecules are present within the membrane?

Answer 8

Phospholipids, cholesterol, channel proteins, carrier proteins, glycoproteins, glycolipids

Question 9

How do proteins move in the bilayer?

Answer 9

Some move sideways while some are in a fixed position

Question 10

What is a glycoprotein?

Answer 10

A protein with a carbohydrate chain attached

Question 11

What is a glycolipid?

Answer 11

A phospholipid with a carbohydrate chain attached

Question 12

What are the parts of a phospholipid?

Answer 12

A hydrophilic phosphate head and a hydrophobic fatty acid tail

Question 13

What does hydrophilic mean?

Answer 13

Attracts water

Question 14

What does hydrophobic mean?

Answer 14

Repels water

Question 15

How do the molecules arrange themselves in a bilayer?

Answer 15

The heads face out towards the water on either side of the membrane and the tails face inwards

Question 16

How does the bilayer act as a barrier to the dissolved substances?

Answer 16

Centre of bilayer is hydrophobic so membrane doesn’t allow water-soluble substances through

Question 17

What is cholesterol?

Answer 17

A type of lipid

Question 18

Where is cholesterol present?

Answer 18

All membranes except bacterial cell membranes

Question 19

Where in the membrane is cholesterol?

Answer 19

Fit between phospholipids and bind to hydrophobic tails causing them to pack more closely together

Question 20

What is the function of cholesterol in the membrane?

Answer 20

Restricts movement of phospholipids and makes membranes less fluid and more rigid, helps maintain shape of animal cells

Question 21

How do you investigate permeability of the cell membrane? (temperature)

Answer 21

1. Use scalpel to cut 5 equal sizes of beetroot
2. Rinse pieces to remove and pigment released during cutting
3. Add pieces to test tubes, each containing 5cm3 of water
4. Place each test tube in water bath at different temperature for same amount of time
5. Remove pieces from test tubes
6. Use a colorimeter
7. Collect data and draw graph

Question 22

How do temperatures below 0 degrees C affect permeability?

Answer 22

• Phospholipids don’t have much energy and can’t move much, packed closely together and membrane is rigid
• Channel proteins and carrier proteins deform and increase membrane permeability
• Ice crystals may form and pierce membrane to make it highly permeable when thaws

Question 23

How do temperatures between 0 and 45 degrees C affect permeability?

Answer 23

• Phospholipids can move around and aren’t packed as tightly together so membrane is partially permeable
• Phospholipids gain energy as temperature increases so permeability is increased

Question 24

How do temperatures above 45 degrees C affect permeability?

Answer 24

• Phospholipid bilayer starts to melt and membrane becomes more permeable
• Water inside cell expands which puts pressure on membrane
• Channel proteins and carrier proteins deform so can’t control what enters or leaves cell which increases permeability